Nissan responds to Leaf owners worries about battery capacity loss

The Nissan Leaf battery pack is supposed to retain 80% capacity after five years, but some Leaf owners in hot areas like Phoenix are reporting nearly that much (sometimes more) capacity loss after one year.

Over the last several weeks some Nissan Leaf owners in Phoenix have reported significant loss of battery pack capacity. The loss of capacity was much steeper than to be expected given the intended 8-10 year lifetime of the Leaf battery packs. Between the level of discussion, and recent news coverage, Nissan's Carla Bailo, senior vice president, Research and Development, sent an open letter to Nissan Leaf owners explaining the situation, and making it clear that Nissan is taking this seriously.

Generally speaking lithium ion batteries do not do well in hot weather, and of course Phoenix and many other cities are known for extremely hot weather. The heat wave this year of course exacerbates worries over the effects of heat on the battery pack. Unlike some of the other electric cars being made, the Nissan Leaf does not have a heating or cooling system on the battery pack leaving no protection against the heat. Nissan's engineers clearly felt it was safe to not have a cooling system, while engineers for other automakers felt otherwise.

A very long discussion thread on mynissanleaf.com identified a dozen or more Leaf owners in not just Phoenix, but other cities in the hot Southwest U.S. who have significant lost battery capacity, some to the tune of 15% capacity loss after one year of ownership. Nissan has repeatedly told Leaf owners to expect 20% capacity loss over 5 years, and clearly losing 15% in one year is a significant worry. According to the summary of the discussion thread, there is no correlation with car color, air conditioned garages, or several other conditions.

A week ago Leaf owners concerns were raised in several news reports including one here on TorqueNews (see Nissan Leaf owners in hot climates experiencing battery problems). As we noted then, this news could spook prospective Leaf owners and be a crushing blow to the Leaf, whose sales were already weak this year.

Carla Bailo's open letter acknowledges the discussion on mynissanleaf.com (and elsewhere) saying "The forum's discussion around battery capacity loss has reached a point where I feel it important to personally address what is being debated, to provide Nissan's viewpoint and, most importantly, to explain the actions we are taking to work with owners."

Bailo claims "only a handful" of battery capacity loss cases exist, and that Nissan is taking the issue seriously. She goes on to explain that "Battery capacity loss of the levels reported may be considered normal depending on the method and frequency of charging." This is a claim which some in the community will be very concerned over, because Nissan's battery warranty covers abnormal capacity loss, not "normal" capacity loss. Whether the capacity loss is normal for a given car depends on, according to Bailo, "the amount of electricity consumed during daily usage and a vehicle's mileage and age." In other words, Bailo implies that a car which is heavily used could see significant battery capacity loss. Typically the lifetime of a battery pack is measured in the number of deep discharge and recharge cycles, not in the calendar age of the pack.

To know for certain Nissan will have to closely examine the customer vehicle, take diagnostic information, to better understand the real-world usage of the cars and the history of specific cars. Nissan does collect some information wirelessly already.

According to Bailo, data already collected through CARWINGS (the onboard software) shows "that less than 0.3 percent of Nissan LEAFs in the U.S. have experienced a loss of any battery capacity bars." Additionally data received globally shows battery capacity loss to affect only high-mileage Leaf's or "those in unique operating situations." The letter doesn't explain that last statement further.

In attempting to explain what can cause battery capacity loss, Bailo first says "All lithium-ion batteries lose capacity with use and age," and that generally "lithium-ion batteries exhibit a higher loss of capacity early in life, with the rate of loss decreasing over time." Factors that could negatively impact (decrease) the life of a given battery pack include "A customer's method and frequency of charging, operating environment, the amount of electricity consumed during daily usage and a vehicle's mileage and age can all affect the rate of battery capacity loss." A fair summary would be to say that if a Leaf is heavily used, driven to the limit every day, it can weaken the battery pack.

Nissan is working to learn more about the specifics of the Leaf's with significant capacity loss, and and whether or not the performance of these cars is within the range of Nissan's expectations. Nissan is committing to work closely with affected customers to discover what has happened, work to identify root causes, and determine the next steps to satisfy the customers.

The letter several times mentions Leaf owners in Arizona, but it is clear from the discussion board that Leaf owners in other states (Texas) are being affected as well.

A key item is whether Nissan considers the capacity loss in the affected cars to be "normal." Leaf owners have been concerned whether Nissan will hide behind claiming the reported capacity loss is "normal." In March, Nissan published a pair of videos on YouTube discussing battery pack warranties and optimal charging practices. Perry explained at that time that "Heat in the range of 130-140F or more is definitely not good for batteries" and describes the concern being long exposure to temperatures in the 120-140F (or hotter) range. At that time I reasoned that there are several cities, like Phoenix, which often have ambient temperatures close to 120F, and that asphalt parking lots have a habit of amplifying the temperature. I closed by asking "is this a problem?" It seems there may indeed be a problem, especially with this years historic heat wave.

This situation calls to mind the recent Nanophosphate EXT announcement from A123 Systems. This new technology is for lithium ion batteries which operate properly in a wider range of temperatures without need for heating or cooling systems. A123 claims the big advantage for Nanophosphate EXT batteries is to eliminate the need for cooling or heating systems to keep battery packs within safe operating temperatures, saving significantly on total system size and complexity. It's likely future electric cars built with this technology would not experience the battery loss capacity some Leaf's are having today.

The issue is not as simple as every Nissan Leaf in Phoenix experiences significant battery capacity loss. Instead it's clear from the forum discussion that some Leaf owners living in hot climates have had no capacity loss.